Golf club

ABSTRACT

A golf club includes a shaft and a head. The shaft has a torque of the entire length of the shaft of from 3 to 5°. In the torsional rigidity distribution of the shaft, an integrated value of the torsional rigidity on the grip end side of the shaft is at least 85% of the integrated value of the torsional rigidity of the entire length of the shaft. The head has a distance to the center of gravity of from 25 mm to 35 mm and has a gravity center angle of from 10° to 20°.

CROSS-REFERENCE TO RELATED APPLICATION

This Application claims priority from Japanese Patent Application No. 2012-071151 filed on Mar. 27, 2012, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a golf club, more particularly to a golf club in which a shaft designed to have a predetermined torsional rigidity and a head designed to have a predetermined center of gravity are combined.

Conventionally, golf club shafts were designed from considerations of torsional rigidity distribution to meet a club head speed depending on the golfer. For example, Japanese Patent Application Publication No. 2008-212340 has disclosed a shaft in which a ratio between the torsional rigidity on the front end side and the torsional rigidity on the grip side is designed within a predetermined range and which enables even a golfer having a capacity of a relatively slow head speed to hit a ball at a large launch angle and expand his or her flying distance.

SUMMARY OF INVENTION

As regards design on the bending rigidity distribution of the shaft, conventionally, extensive research and development have been carried out. However, regarding the torsional rigidity of the shaft (usually measured and evaluated as a torque), although there is some research and development which handle the torsional rigidity of the entire shaft length, the distribution of the torsional rigidity of the shaft has been of little attention. The shaft is in such a cylindrical shape that its diameter decreases toward the front end from the grip side of the shaft. Therefore, as for the distribution of the torsional rigidity of the shaft, usually, the torsional rigidity decreases gradually toward the front end from the grip side of the shaft. When a golfer swings a golf club, torsion of the shaft occurs mainly on the front end side of the shaft. However, a professional golfer feels no problem in the shaft having such a torsional rigidity distribution.

According to research on the torsional rigidity distribution of the shaft, the inventor of the present invention has found that changing the torsional rigidity distribution of the shaft from that of a conventional one allows an amateur golfer to improve the operability of his or her golf club. In addition, it has been found that when the torsional rigidity distribution of the shaft is changed, arranging the center of gravity of the head under a predetermined configuration improves the direction of a hit ball and stabilizes the head behavior so that the golfer can obtain a firm feeling of hitting the ball.

The present invention aims at providing a golf club which allows an amateur golfer to improve the operability thereof, stabilize the direction of a hit ball and obtain a firm feeling of hitting the ball.

To achieve the above-described object, the present invention provides a golf club comprising a shaft and a head, wherein the shaft is so constructed that the torque of an entire length of the shaft is in a range of 3 to 5°, wherein in the torsional rigidity distribution of the shaft, an integrated value of the torsional rigidity on the grip end side of the shaft is 85% or more of the integrated value of the torsional rigidity of the entire length of the shaft, wherein the head is so constructed that the distance to the center of gravity is in a range of 25 to 35 mm and the gravity center angle is in a range of 10 to 20°.

According to the present invention, the measuring method for the torque of the entire length of the shaft includes fixing the shaft at a position 1,040 mm from the front end of the shaft and turning the shaft with a force of 1 ft-lb. (0.1383 kgf·m) applied to a position 25 mm from the front end of the shaft in order to measure a twisted angle of the shaft. The measuring method for the torsional rigidity distribution of the shaft includes fixing the shaft at positions 200 mm, 400 mm, 600 mm, 800 mm, 1,000 mm from the front end of the shaft and turning the shaft with a force of 1 ft-lb. (0.1383 kgf·m) applied to a position 25 mm from the front end of the shaft in order to measure the twisted angle of the shaft and calculate the torsional rigidity at each measurement position. The integrated value of the torsional rigidity of the entire length of the shaft is a value obtained by integrating the torsional rigidity from 200 mm from the front end of the shaft to 1,000 mm from the front end of the shaft. The integrated value of the torsional rigidity on the grip end side of the shaft is a value obtained by integrating the torsional rigidity from 400 mm from the front end of the shaft to 1,000 mm from the front end of the shaft.

The weight of the shaft may be 50 g or more.

As described above, the present invention defines the torque of the entire length of the shaft to be in the range of 3 to 5° and in the torsional rigidity distribution of the shaft, the integrated value of the torsional rigidity on the grip end side of the shaft to be 85% or more the integrated value of the torsional rigidity of the entire length of the shaft. As a result, in the torsion of the entire shaft, the torsion of the shaft on the grip end side is relatively small and the torsion of the shaft on the front end is relatively large, so that the operability of the golf club is improved for an amateur golfer. Furthermore, because the torsion of the shaft on the grip end side is relatively small, combining a head in which the distance to the center of gravity is in a range of 25 to 35 mm and the gravity center angle is in a range of 10 to 20° with the aforementioned shaft stabilizes the direction of a hit ball and makes a golfer obtain a firm feeling of hitting a ball.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing an example of a golf club according to the present invention;

FIG. 2 are views for describing a method for measuring a torque of a golf club shaft while FIG. 2A is a plan view thereof and FIG. 2B is a perspective view thereof;

FIG. 3 is a graph for describing a distribution and sum of the torsional rigidity of a shaft;

FIG. 4 is a front view for describing a distance between the center of gravity of a golf club head and the axis of its shaft;

FIG. 5 is a plan view of a golf club head for describing an angle of the center of gravity; and

FIG. 6 is a graph showing the torsional rigidity distributions of the shafts according to an example of the present invention and a shaft according to a comparative example.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, an embodiment of a golf club according to the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the golf club of the present embodiment includes a shaft 1, a head 2 and a grip 8. The shaft 1 has a cylindrical shape in which the diameter thereof decreases gradually toward a front end 1T from a grip end 1B. A head 2 is attached to the front end 1T of the shaft 1 and a grip 8 is attached to the grip end 1B.

The length of the shaft 1 mentioned here may be an ordinary length of a shaft for a fairway wood or a utility club, and more particularly, is preferred to be 37.0 to 44.0 inches (939 to 1,118 mm). A required diameter of the shaft 1 may be an ordinary diameter of the shaft for the fairway wood or the utility club. More specifically, the outside diameter on the grip end side is preferred to be 14.0 to 16.0 mm and the outside diameter on the front end side is preferred to be 8.5 to 9.5 mm. The weight of the shaft 1 is preferred to be in a range of 50 to 80 g as the shaft for the fairway wood or the utility club, and is more preferably 60 to 75 g.

The torsional rigidity distribution of the shaft 1 is so configured that the integrated value of the torsional rigidity on the grip end 1B side of the shaft is much higher than the integrated value of the torsional rigidity of an entire length of the shaft, compared to conventionally. More specifically, the torque of the entire length of the shaft 1 is set in a range of 3 to 5° and the integrated value of the torsional rigidity on the grip end 1B side of the shaft is set to be 85% or more the integrated value of the torsional rigidity of the entire length of the shaft. When an amateur golfer hits a ball with his or her golf club having such a configuration, the torsion of the shaft 1 of the golf club on the grip end side is relatively small, thereby enhancing the operability of the golf club. In the meantime, the ratio of the integrated value is preferred to be 86% or more. Although the upper limit of the integrated value is not limited to any particular values, it is preferred to be 96% or less.

Here, a measuring method for the torque of the shaft 1 will be described with reference to FIGS. 2A and 2B. As for the measuring method for the torque of the entire torque length, a portion after 1040 mm from the front end 1T of the shaft 1 is fixed with a fixing member 40 (that is, a measuring span L from the front end 1T of the shaft up to the fixing member 40 is 1040 mm), and a jig 30 having a length of 50 mm is attached to a portion 50 mm long from the front end 1T. An arm 31 having a length of 1 ft is provided at a central position of the jig 30, namely, at a position 25 mm from the front end 1T of the shaft 1 in a direction perpendicular to the longitudinal direction of the shaft. Then, a weight 32 having a weight of 1 lb is provided at the front end of the arm 31. Thus, the shaft 1 is twisted with a force of 1 ft-lb (0.1383 kgf·m) applied to a position 25 mm from the front end 1T thereof. Then, the twisted angle of the shaft 1 is measured. This measured value is a torque value of the entire shaft length.

Next, a measuring method for the torsional rigidity of the shaft will be described. According to this measuring method also, the shaft is twisted with a force of 1 ft-lb applied to the position 25 mm from the front end 1T of the shaft 1 in the same way as the measuring method for the torque. In this case, the fixing member 40 is fixed under a plurality of measuring spans L, namely, at a plurality of positions selected between the front end 1T side of the shaft and the grip end 1B. Then, the twisted angle is measured when the fixing member is fixed at each position. From the measured twisted angle, a torsional rigidity under each measuring span L is calculated according to the following equations.

GI=Mt/Φ

Φ=θ/L

-   GI: torsional rigidity (kgf·m²/rad) -   Mt: load (kgf·m) -   θ: twisted angle (rad) -   L: measuring span (m)

As a result, as shown in FIG. 3, a torsional rigidity distribution of the shaft under the measuring span L, namely, at a length from the front end 1T of the shaft is obtained. In measuring the torsional rigidity, the more measuring spans are prepared, the more accurate torsional rigidity distribution can be obtained. However, by preparing the measuring spans L at five positions 200 mm, 400 mm, 600 mm, 800 mm, 1,000 mm as shown in FIG. 3, a sufficiently accurate torsional rigidity distribution can be obtained. In this torsional rigidity distribution, an integrated value GI_(W) of the torsional rigidity of the entire shaft length is a value obtained by integrating the torsional rigidities from 200 mm to 1,000 mm in the measuring span L. Further, an integrated value GI_(B) of the torsional rigidity on the grip end side of the shaft is a value obtained by integrating the torsional rigidities from 400 mm to 1,000 mm in the measuring span L. In this torsional rigidity distribution, the torsional rigidities of adjacent measuring spans are collinearly approximate to each other. Thus, integration of the torsional rigidity distribution can be performed by calculating an area of a trapezoid formed between adjacent measuring spans (e.g., an area between 200 mm and 400 mm) as shown in FIG. 3.

In the torsional rigidity distribution of the shaft, an integrated value of the torsional rigidities from 600 mm to 1,000 mm in the measuring span L is preferred to be 75% or more the integrated value GI_(W) of the torsional rigidity of the entire shaft length. Although the upper limit of the ratio of this integrated value is not restricted to any particular value, preferably, it is 90% or less. Furthermore, an integrated value of the torsional rigidity from 800 mm to 1,000 mm in the measuring span L is preferred to be 45% or more of the integrated value GI_(W) of the torsional rigidity of the entire shaft length. Although the upper limit of the ratio of this integrated value is not restricted to any particular value, preferably, it is 60% or less.

In the meantime, the torsional rigidity distribution of the shaft is not limited to a distribution in which the torsional rigidity increases gradually from the front end side of the shaft to the grid end side, but may be a distribution having an area in which the torsional rigidity decreases gradually from the front end side of the shaft to the grip end side. Such an area may be provided in, for example, a portion 400 mm to 600 mm from the front end of the shaft. The torque of the entire shaft length may be relatively firm and if a further operability and stability are demanded, preferably, it is in a range of 3 to 4°

The shaft 1 is manufactured according to Sheet Winding Method. Explained in detail, a prepreg sheet of fiber reinforced plastic (FRP) is wound around a mandrel (not shown) and is hardened by heat, and after that, the mandrel is pulled out of the hardened product to finish the shaft 1. As the reinforced fiber for the fiber reinforced plastic, it is permissible to use only carbon fiber alone or composite fiber made of carbon fiber and other material fibers, or metallic fiber. Furthermore, as matrix resin, thermoplastic resin such as epoxy resin may be used.

In the prepreg sheet for use, its fibers are oriented substantially in a single direction. When fibers are arranged in parallel to the axis line of the shaft, a straight layer is formed, and when fibers are arranged obliquely, a bias layer is formed. The prepreg sheet for the bias layer is oriented at an angle of 45°, for example, with respect to the shaft axis line of the shaft. Usually, for the bias layer, prepreg sheets are wound in two layers such that orientation angles of their fibers are inclined in an opposite direction to each other, shifted by an amount corresponding to half a circumference to each other.

The prepreg sheet includes a main sheet having the same length as the entire length of the shaft 1 and a reinforcement sheet which is shorter than the entire length of the shaft. Because the mandrel is tapered such that the diameter thereof increases toward the grip end from the front end, the main sheet is formed in a trapezoidal shape in which a side on the grip end side is longer in order to allow a predetermined circumference of the sheet to be wound equally around the mandrel. The main sheet for the straight layer may be formed into a pentagonal shape by cutting a side of the trapezoid in the midway in order to reduce the number of windings on the grip end side compared to the front end side. Although the reinforcement sheet may be formed into the trapezoidal shape also, it may be formed into a rectangle in which the side on the grip end side is oblique or a triangle in order to obtain a predetermined bending rigidity distribution. Usually, the reinforcement sheet is used for the straight layer.

To produce a shaft which attains the torsional rigidity distribution of the present invention independently of the bending rigidity distribution of the shaft, the main sheet for the bias layer is formed into a trapezoidal shape in which the side on the grip end side is longer than ordinary trapezoids, in order to increase the number of windings on the grip end side gradually compared to the front end side. For example, a sheet which approximately doubles the number of windings on the shaft grip end side compared to that on the front end side of the shaft may be used. By using the prepreg sheet having such a configuration, the torsional rigidity on the front end side may be decreased with a design on the bending rigidity distribution of the shaft maintained as much as possible.

In addition, as the main sheet for the bias layer, instead of using a sheet having the same length as the entire length of the shaft 1, the sheet may be divided to two sections for the front end side and the grip end side such that the length of those two sheets is equal to the entire length of the shaft 1. In this case, the elastic modulus of the sheet on the front end side may be higher than the elastic modulus of the sheet on the grip end side. For example, the elastic modulus of the sheet on the grip end side may be 1.1 to 2.0 times the elastic modulus of the sheet on the front end side. Such a configuration also can secure the same advantage as described above.

In the head 2 for use, a distance to the center of gravity is in a range of 25 to 35 mm. As shown in FIG. 4, the distance to the center of gravity mentioned here refers to a distance from a shaft axis line S which is a central line of a hosel 5 of the head 2 up to the center of gravity C of the head. More preferably, the distance to the center of gravity is in a range of 27 to 33 mm.

In the head 2 for use, the gravity center angle is in a range of 10 to 20°. As shown in FIG. 5, the gravity center angle mentioned here refers to an angle formed between a line passing through both the shaft axis line S and the head gravity center C and a tangent line F on a face surface 3 of the head. More preferably, the gravity center angle is in a range of 14 to 18°.

Combination of the head 2 having the distance to the center of gravity and the gravity center angle in the above-mentioned ranges with the shaft 1 having the above-described bending rigidity distribution enables an amateur golfer to stabilize the direction of a hit ball with a high operability of a club secured, and obtain a firm feeling of hitting a ball.

EXAMPLES

Shafts of examples 1 to 5 and comparative examples 1 to 4 having torsional rigidity distributions and torques of the entire shaft length indicated in Table 1 were manufactured and tested by hitting a ball. Table 2 shows a ball flying distance of each case and an evaluation by a testing golfer who hit a ball with the golf club. Table 2 indicates an integrated value (GI_(W)) of the torsional rigidity of the entire shaft length, calculated from the torsional rigidity distribution in Table 1, an integrated value (GI_(B)) of the torsional rigidity on the grip end side and a ratio therebetween (GI_(B)/GI_(W)). FIG. 6 indicates the torsional rigidity distributions of the shaft according to example 1 and comparative example 1. As indicated in FIG. 6, the shaft 1 of example 1 had a distribution in which the torsional rigidity on the grip end side was lower compared to the shaft according to comparative example 1. In the meantime, each of all the shafts was combined with an identical head. The distance to the center of gravity is 30 mm and the gravity center angle is 15°.

TABLE 1 Torque of Torsional rigidity [kgf · m²/rad] entire length L = 200 mm L = 400 mm L = 600 mm L = 800 mm L = 1000 mm [°] Example 1 0.70 1.22 3.17 7.92 7.92 4.0 Example 2 1.98 1.76 1.76 3.96 15.84 3.0 Example 3 0.91 1.58 0.79 7.92 7.92 4.8 Example 4 0.91 1.76 2.64 15.84 15.84 3.1 Example 5 0.63 1.22 1.44 7.92 7.92 4.8 Comparative 1.49 3.96 1.32 2.64 3.96 3.5 example 1 Comparative 1.98 2.64 1.98 7.92 3.17 2.8 example 2 Comparative 1.08 1.44 0.59 15.84 5.28 5.4 example 3 Comparative 1.19 1.58 3.17 0.79 1.76 5.5 example 4

TABLE 2 Torsional rigidity Integrated Integrated value of value on Ratio entire grip end (GI_(B)/ Evaluation length side GI_(W)) Directional by testing (GI_(W)) (GI_(B)) [%] property golfer Example 1 3.32 3.13 94.3 5 5 Example 2 3.28 2.90 88.4 4 4 Example 3 2.94 2.69 91.5 4 4 Example 4 5.72 5.46 95.5 4 5 Example 5 2.97 2.79 93.9 5 4 Comparative 2.13 1.58 74.2 3 4 example 1 Comparative 3.02 2.56 84.8 4 2 example 2 Comparative 4.21 3.96 94.1 2 3 example 3 Comparative 1.40 1.13 80.7 1 2 example 4

An evaluation of the directional property in Table above indicates a probability that a hit ball may fly in an intended direction and has five grades in which “5” is the highest and “1” is the lowest. An evaluation by a testing golfer concerns the operability of a club during a swing and a golfer's feeling of hitting a ball (a feeling that the head may turn back securely when it hits a ball) and has five grades in which “5” is the highest and “1” is the lowest.

As shown in Table 2, clubs of examples 1 to 5 were evaluated as 4 or higher in the directional property and the sensory test. On the other hand, comparative example 1, which was evaluated low in the torsional rigidity on the grip end side although its entire torque was equal to the above examples, was evaluated as 3 because the direction of a hit ball was not stabilized. In the meantime, a testing golfer could make an impact timing easily and thus, the sensory test was evaluated as high as 4. Comparative example 2, in which the entire torque was low and the torsional rigidity on the grip end side was low, was evaluated as 4 because the directional property was stabilized, however in the sensory test, the testing golfer felts hardness in the entire shaft and evaluated severely that the club of comparative example 2 was difficult to make an impact timing. Comparative example 3, in which the entire torque was too high although the torsional rigidity on the grip end side was equal to the above examples, was evaluated as 2 because the direction of a hit ball was unstable. In the sensory test, the testing golfer evaluated the club of comparative example 3 as 3 because it was felt that the entire head behavior was large although firmness was felt in the shaft. In comparative example 4 in which the entire torque was too high while the torsional rigidity on the grip end side was low, the direction of a hit ball was very unstable and thus the club was evaluated as 1. In the sensor test, the testing golfer made a severe evaluation because a movement of the shaft on the grip end side was felt to be soft so that the club was not stabilized.

Clubs in which the shafts of example 1, example 3 and comparative example 3 were combined with the heads having the distance to center of gravity and the gravity center angle shown in Table 3 were tested by hitting balls. The results are shown in Table 3. The “catch” in the table means a testing golfer's evaluation concerning how effectively the head of a given club can catch a ball. The catch was evaluated according to the five grades in which “5” is the highest and “1” is the lowest.

TABLE 3 Distance to Gravity Evaluation center of center angle Directional by testing gravity [mm] [°] Shaft property Catch golfer Example A 30 15 Example 1 5 4 5 Example B 29 12 Example 1 4 3 4 Example C 32 16 Example 3 5 4 4 Example D 33 19 Example 1 4 5 3 Comparative 23 18 Example 1 2 3 3 example A Comparative 32 9 Example 1 3 1 2 example B Comparative 35 23 Comparative 2 4 1 example C example 4

As indicated in Table 3, the clubs of examples A to D entirely maintained a high evaluation in terms of the directional property and sensory tests. On the other hand, according to the sensory test, comparative example A in which the shaft of example 1 was combined with the head having a short distance to the center of gravity was unstable in terms of the directional property, although the operability was not bad and was evaluated as 3. In the sensory test, comparative example B, in which the shaft of example 1 was combined with the head having a small gravity center angle, made the testing golfer feel a difficulty in swinging and was evaluated bad at catching the ball. Regarding comparative example C in which the shaft of comparative example 4 was combined with the head having a large gravity center angle, it was evaluated that the directional property of the club was low, its head behavior was large and it was heavy to swing smoothly although it caught the ball excellently. 

What is claimed is:
 1. A golf club comprising: a shaft having a torque of an entire length of the shaft of from 3° to 5°, wherein in a torsional rigidity distribution of the shaft, an integrated value of a torsional rigidity on a grip end side of the shaft is at least 85% of a integrated value of a torsional rigidity of the entire length of the shaft, wherein a measuring method for the torque of the entire length of the shaft includes fixing the shaft at a position 1,040 mm from the front end of the shaft and turning the shaft with a force of 1 ft-lb (0.1383 kgf·m) applied to a position 25 mm from the front end of the shaft in order to measure a twisted angle of the shaft, wherein the measuring method for the torsional rigidity distribution of the shaft includes fixing the shaft at positions 200 mm, 400 mm, 600 mm, 800 mm, 1,000 mm from the front end of the shaft and turning the shaft with a force of 1 ft-lb (0.1383 kgf·m) applied to a position 25 mm from the front end of the shaft in order to measure the twisted angle of the shaft and calculate the torsional rigidity at each measurement position, wherein the integrated value of the torsional rigidity of the entire length of the shaft is a value obtained by integrating the torsional rigidity from 200 mm from the front end of the shaft to 1,000 mm from the front end of the shaft, wherein the integrated value of the torsional rigidity on the grip end side of the shaft is a value obtained by integrating the torsional rigidity from 400 mm from the front end of the shaft to 1,000 mm from the front end of the shaft; and a head having a distance to a center of gravity of from 25 mm to 35 mm and having a gravity center angle of from 10° to 20°.
 2. The golf club according to claim 1, wherein the shaft having a weight of at least 50 g. 